1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to a method and apparatus for casting a prosthetic socket under vacuum.
2. Description of the Prior Art
The making of a prosthetic socket begins with a prosthetist taking a negative cast of an amputee's stump, also known as a residual limb. Filling the negative with plaster then makes a positive.
The positive is then reduced by a factor depending upon the physiology of the residual limb so that the prosthetic socket will fit properly thereon. Typically, the amount of reduction is 3% to 10%, depending upon the maturity of the residual limb, the amount of redundant tissue, the gender of the patient, the vascular history of the patient, and other such considerations. Layers of plaster are removed by hand using blades and scraping tools until the desired reduction is achieved. The layer removed should be as uniform as possible.
U.S. Pat. No. 5,503,543 discloses a pressure-casting machine used in the industry to provide a more uniform reduction. The machine displaces fluid from a residual limb by applying a uniform pressure thereto between 80–300 mm Hg for a predetermined amount of time. Sufficient fluid is displaced from the residual limb to ensure that the negative cast made from the casting will be of the desired size.
One drawback of pressure type casting machines is that manipulation of the residual limb during the hardening of the cast cannot be performed when such a machine is used. Another drawback arises from the fact that when pressure is applied to the bladder, the machine pushes itself away from the residual limb. This phenomenon occurs because the proximal end of the residual limb lacks an equivalent section of pressurized bladder to match the force exerted by the pressure in the bladder at the distal end of the residual limb.
The force pushing the bladder away from the patient must equal the force applied by the amputee onto the pressure bladder. However, the force exerted by the amputee is not perfectly controllable. Accordingly, variations occur in the casting process, resulting in variations in the dimensions of the negative cast.
In performing the steps of the above-described casting process, the prosthetist puts a prosthetic liner on a residual limb and then wraps a plastic separator known as a cling wrap over the liner. If a liner is not used, the cling wrap is applied directly to the residual limb. Plaster bandages that have been soaked in water are then wrapped around the residual limb.
As an alternative to such plaster bandages, a urethane-impregnated fabric that has been soaked in water may be used in place of the plaster bandages. The urethane reacts with the water and turns the fabric into a rigid structure. Urethane-impregnated fabrics have been used for years by prosthetists in the making of immobilization casts.
In the description and claims that follow, terms such as “plaster means” or “plaster bandage means” should be understood as including urethane-impregnated fabric as well.
The steps then change depending upon whether the job is to be completed by hand or by machine.
If the job is to be completed by hand, the prosthetist manipulates the plaster by hand to provide the modifications to the geometry of the plaster as deemed appropriate for the physiology of the residual limb. Significantly, this hand manipulation of the plaster is performed while the plaster is hardening.
After the plaster has hardened, the negative cast is cut longitudinally and removed from the residual limb. Pouring plaster into the negative then produces a positive.
When the positive has hardened, blades and scraping tools are used to manually reduce the circumference of the positive as uniformly as possible along its length, section by section. Although the reduction process is laborious, it retains the geometry of the modifications imparted at the time of casting.
A properly fitting prosthetic socket is produced from the modified cast by thermoforming a thermoplastic sheet over the positive cast or by laminating a carbon-epoxy matrix over the positive cast.
If the job is to be completed by machine, the prosthetist wraps the plaster in cling wrap, places the wrapped stump in a pressure-casting bladder and applies adequate pressure for a predetermined amount of time. This causes the plaster to harden into a negative cast. The negative cast is then cut longitudinally and removed from the residual limb. Pouring plaster into the negative cast then produces a positive.
When the positive has hardened, the prosthetist makes the necessary modifications according to the physiology of the residual limb by adding plaster where needed or by carving our sections of the positive cast. The modifications must be made on the hardened positive cast because the pressure bladder prevents manipulation of the residual limb while the plaster is hardening.
A properly fitting prosthetic socket is made from the modified cast by thermoforming a thermoplastic sheet over the positive cast or by laminating a carbon-epoxy matrix over the positive cast.
A prosthetic casting machine is therefore needed that would allow manipulation of the plaster means while the negative cast is hardening.
Moreover, there is a need for a positive casting machine that would allow the application of positive pressure on the negative cast while the plaster means is hardening.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.